Table of Content

28 February 2024, Volume 30 Issue 1

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Estimation of environmental parameters of Yungang Grottoes based on empirical mode decomposition and long short-term memory artificial neural network

LU Baoming, XU Jinming

2024, 30(1):  1-016.  doi:10.12066/j.issn.1007-2861.2409

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The weathering process of grottoes is directly influenced by environmental parameters. Consequently, estimating these parameters is important for the effective preservation of Yungang Grottoes. This research utilized measured time-series data of wall temperature, environmental humidity, and temperature from the 10th grotto of Yungang Grottoes. These data were decomposed into various components using empirical mode decomposition (EMD). Correlations between the measured time-series data and intrinsic mode function (IMF) components were also investigated. A combined model, based on the EMD-long short-term memory (LSTM) artificial neural network (ANN), was then developed. Using mean absolute error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE), and R² as the evaluation indices, comparisons were made be- tween the recorded environmental parameters and those estimated by the combined model and standalone LSTM-based ANN. The findings suggested that as the rate of change in the IMF components increased, the correlation between the IMF components and measured time-series increased. When only employing the LSTM-based ANN, optimal results were obtained with 2 hidden layers and an initial learning rate of 0.001. Conversely, when using the combined model, MAE, RMSE, and MAPE values decreased, while R² values in- creased, indicating the improved estimation efficiency. The accuracy of the environmental parameter estimations largely depended on the extent of parameter changes, with smaller changes leading to better model efficiency. The insights gained from this research can be useful for the preservation of cultural relics of grottoes.



Damage characteristics and weathering evaluation of Yungang Grottoes sandstone under freeze-thaw

GAN Zhixin, HUANG Jizhong, ZHANG Yue, LUO Qingyang, ZHANG Ruoyu, DU Houmeng,

2024, 30(1):  17-030.  doi:10.12066/j.issn.1007-2861.2485

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Weathering of Yungang Grottoes sandstone is significant under freeze-thaw conditions. To understand the change of damage and weathering degree of sandstone under freeze-thaw, this study simulates the weathering process of Yungang Grottoes sandstone by indoor freeze-thaw cycle tests. Sandstone with different weathering degrees can be obtained by setting different freeze-thaw cycle times under saturated conditions. Before the start of cycles and after every 5 cycles, a number of macroscopic nondestructive testing techniques are used to test the sandstone. Subsequently, the failure characteristics, and changes of physical and mechanical properties of sandstone during the freeze-thaw cycle are obtained. The damage mechanism of internal structure and the reason of property index change are discussed from the macroscopic perspective by combining with microscopic detection technology. Moreover, the weathering degree of sandstone is determined according to the wave velocity ratio. The results indicate particle disintegration of sandstone, which results in the gradual destruction of the structure forming cracks. In addition, the weathering degree of sandstone gradually deepens and the sandstone reaches medium weathering degree after 60 cycles. The results of various detection methods indicate certain regularity: the mass, ultrasonic wave velocity, content of Si and Ca, and compressive strength of sandstone decrease with the increase of freeze-thaw cycles, and the pores of the sandstone are increasing. It is found that a specific correlation exists between the number of freeze-thaw cycles, ultrasonic wave velocity, and compressive strength of sandstone. The formula between the three values is established and can be directly applied.



Preparation of Y³⁺-doped silica abrasives and the chemical mechanical polishing behavior of zirconia ceramics

DAI Sanwei, LEI Hong, FU Jifang

2024, 30(1):  31-042.  doi:10.12066/j.issn.1007-2861.2390

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To improve the polishing efficiency of zirconia ceramics, Y³⁺ was doped on the surface of silica to obtain modified abrasives. X-ray photoelectron spectroscopy (XPS) analysis showed that the Y element exists in the modified abrasive in the form of Y(OH)₃. Results of scanning electron microscopy (SEM) and particle size analysis showed that the composite abrasives were spherical with a uniform particle size, and no aggregation and secondary particles appeared. Compared with the pure colloidal silica abrasive, the material removal rate (MRR) of the composite abrasives was increased by approximately 33%. It also changes the zeta potential of the silica particles and reduces the repulsion between the silica and zirconia ceramic surface. This increases the contact probability between the silica and zirconia ceramic wafer, resulting in an increase in the coefficient of friction.



Thickness selection of Bi₂O₃ electrochromic films

WU Hao, ZHAO Jiadong, LIU Chunyu, YU Shengwen

2024, 30(1):  43-053.  doi:10.12066/j.issn.1007-2861.2323

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It is necessary to select appropriate thickness for the fabrication of Bi₂O₃ thin films with reasonable electrochromic properties. Bi₂O₃ thin films with an approximate range of 20∼300 nm in thickness were prepared by magnetron sputtering. The electrochromic properties of the films were analyzed by using ultraviolet-visible (UV-Vis) spectrophotometry and an electrochemical workstation. The surface morphology and phase structure of the thin films were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). After comprehensive screening to assess their performance in terms of the color change contrast (∆Tλ=550 nm), electrochromic efficiency (η), and performance retention (R∆T , R_η ), the values of ∆T and η of Bi₂O₃ thin films with a thickness between 60 nm and 120 nm were found to reach 25% and 10 cm²/C, respectively. Furthermore, the retention of the electrochromic properties (R∆T = 20%, R_η = 44.6%) is high. This may be related to the fact that the main phase of the film in this thickness range is δ, which is characterized by high ionic conductivity.



Preparation and photocatalytic performance of Co₃O₄/SnO₂ derived from metal organic framework

WU Hanhong, LIU Shanxin, Wang Dawei, HUANG Ruting, CHEN Zhiwen

2024, 30(1):  54-067.  doi:10.12066/j.issn.1007-2861.2330

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A cubic  Co₃O₄/SnO₂ composite photocatalyst was prepared by combining do-decahedral nano-blocks derived from metal-organic framework (MOF) material ZIF-67 with SnO₂ at room temperature. Results showed that the band gap of the calcined  Co₃O₄/SnO₂ material was significantly reduced, and the phenomenon of fluorescence quenching was obvious. The addition of Co3O4 expanded the photoresponse range of SnO₂ to visible light or even infrared light and simultaneously promoted the separation of photo-generated carriers during the photocatalytic reaction. With Rhodamine B (RhB) used as the target reactant, the photocatalytic degradation activity of  Co₃O₄/SnO₂ derived from the MOF was investigated under visible light. It was found that  Co₃O₄/SnO₂ could degrade 89.6%RhB within 60 min, which was 4.5 and 3 times greater than those of pure SnO2 and pure ZIF-67, respectively. In addition, Co3O4/SnO2 showed good photoreactivity and stability. Based on these experimental results and those from free-radical quenching experiments, the mechanism of photocatalytic degradation of organic dyes RhB by the MOF-derived Co3O4/SnO2 composite material was proposed.



Syntheses and Photochromic properties of 4-fluoroacetophenone disubstituted viologen

ZHANG Haotian, BAI YueLing, HANG Xiangcao, AN BaoLi, XU Jiaqiang

2024, 30(1):  68-076.  doi:10.12066/j.issn.1007-2861.2301

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Owing to their sensitive chromic behaviour under external stimulation, such as light, heat, and electricity, viologen-based materials have shown considerable potential in optical switching and molecular sensor recognition applications. 4-Fluoroacetophenone disubstituted viologen (VioF₂·2Cl) was synthesised via a one-step reaction. The introduction of fluoroacetophenone substituents expands the conjugated system of the molecule which stabilises the radical structure and facilitates retention of the colour change for a longer period of time. The synthesized VioF2·2Cl exhibited sensitive photochromic properties, showing a rapid colour change from white to light yellow and then to yellow-green under ultraviolet (UV) light irradiation. Analysis of the crystal structure confirmed that the VioF2+ 2 molecules possess a shorter π · · · π∗ interaction distance after discoloration, which induces photoinduced electron transfer (PET) and thus stabilizes the viologen radical. VioF2·2Cl crystals can maintain their coloured radical state in an oxygen environment for three days without significant fading. This novel viologen derivative exhibits better sen- sitive photochromic properties and free radical colour stability essential for its application in the field of photochromic materials.



Enhanced denitrification effect of biological rope by composite solid-phase carbon source materials

Li Ziru, Wang Feifei, Pan Jiazheng, Hu Yulin, He Chiquan, Huang Xin

2024, 30(1):  77-085.  doi:10.12066/j.issn.1007-2861.2337

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There are few organic carbon sources in micro-polluted water with excessive total nitrogen. Adding an external carbon source can promote denitrification to remove nitrogen. Solid carbon sources have attracted attention because they overcome the shortcomings of the traditional carbon source. In this study, two solid carbon sources, PSPC-Ⅰ and PSPC-Ⅱ, were prepared by cross-linking, using agricultural waste corncob and polymer materials as carbon sources and polyvinyl alcohol and sodium alginate as skeleton carriers. The carbon release characteristics of the two solid carbon sources and their enhanced denitrification effect were studied. The results showed that the two solid carbon sources released carbon continuously and did not reach carbon release equilibrium within 28 days. The maximum carbon release values of PSPC-Ⅰ and PSPC-Ⅱ were 6.3 and 8.7 mg/g (calculated via the dissolved organic carbon (DOC)), respectively. Three-dimensional fluorescence results showed that the released carbon sources were mainly soluble microbial metabolites and aromatic proteins that were easily degraded by microorganisms. In comparison with the biological rope without an added carbon source (6 200 ng/g, calculated via the adenosine triphosphate (ATP)), both solid carbon sources significantly increased the biomass of biological rope biofilm (PSPC-Ⅰ: 400∼600 ng/g, PSPC-Ⅱ: 300∼500 ng/g). Additionally, both solid carbon sources significantly enhanced denitrification. The control group did not produce denitrification, but the denitrification rates of the two solid carbon sources were as high as 80.4% and 75.0%, respectively.



The Optimal Selection of Remediation Plants for Cd Contaminated River Sediment

SHEN Jiayi, ZANG Xueke, ZHANG Changsong, GAO Bingjie, GAO Mingjing, LI Xinyi, ZHANG Xinying

2024, 30(1):  86-093.  doi:10.12066/j.issn.1007-2861.2336

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Twelve plants were selected to conduct an experimental study on remediation of Cd contaminated sediment of black-odor river in Shanghai. Tolerance, enrichment and translocation features, and remediation efficiencies of plants to the heavy metal were investigated, with a view to find practical application of phytoremediation of river sediments polluted by Cd. Results revealed that all the plants except the transplanted Juncus effusus L. showed good tolerance to the sediment. The above-ground Cd contents of Solanum nigrum L., Juncus effusus L., Calendula officinalis L., Hylotelephium erythrostictum (Miq.) H. Ohba, and Farfugrium japonicum (L. f.) Kitam. were higher than 4.50 mg/kg. The bioaccumulation factors (BCFs) and translocation factors (TFs) of Cd in Abutilon theophrasti Medicus, Juncus effusus L., Calendula officinalis L., Hylotelephium erythrostictum (Miq.) H. Ohba, Farfugrium japonicum (L. f.) Kitam. and Phytolacca americana L. were greater than 1. The extraction amounts of Cd in Solanum nigrum L., Calendula officinalis L., Phytolacca americana L. and Bidens pilosa L. were higher than 0.30 kg/hm², and had relatively good remediation effects. Among the plants, the extraction amount and extraction efficiency of Solanum nigrum L. for Cd in the sediment were up to 2.84 kg/hm² and 88.75%, respectively, indicating great remediation potential. The optimization test proved that Solanum nigrum L., as the best remediation plant, could be used to remediate the Cd contaminated river sediment in this area.



Lightweight traffic-light detection algorithm based on improved YOLOv5s

CAI Guanhong, LI Guoping, WANG Guozhong, TENG Guowei

2024, 30(1):  94-105.  doi:10.12066/j.issn.1007-2861.2411

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A lightweight traffic-light detection algorithm based on improved YOLOv5s is proposed to solve the issue of numerous network model parameters and poor real-time performance of current traffic-light detection algorithms. First, a lightweight network, Mo- bileNetv3, is used to replace the original backbone network, and the attention mechanism is introduced to reduce the number of model parameters on the premise of minimal impact on detection accuracy. Next, the depth separable convolution is used to replace the traditional standard convolution in the neck network to further reduce the number of model parameters. Subsequently, the detection layer for detecting large targets is deleted based on the small scale of traffic lights. Finally, the frame regression loss function is improved to improve the frame detection accuracy. The network is pruned to compress and accelerate the model to be deployed on the embedded platform in real time. The experimental results show that the proposed algorithm can achieve a detection speed of 48.1 frame/s on the embedded platform NVIDIA Jetson Xavier NX, which sacrifices 1.5% mAP compared with the original YOLOv5s. However, the model size is compressed by 54.3%, and the detection speed is increased by 2.6 times, which can satisfy the needs of real-time traffic-light detection on traffic roads.



Applications of ϕ-mapping theory in describing Weyl topological semimetals

HUANG Xiaohong, JIANG Ying

2024, 30(1):  106-117.  doi:10.12066/j.issn.1007-2861.2392

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In this study, we examine the topological classification of Weyl semimetals of Hermitian and non-Hermitian systems using ϕ-mapping topological current theory. We establish the ϕ fields in the momentum space by the given Hamiltonians of two-band systems to define the topological charge density. We find that the topological charge density is nonzero only at the zeroes of the norm of the ϕ fields, and these zeroes are exactly where Weyl points or Weyl exceptional points are located. The quantized numbers obtained by integrating the topological charge density can be used as the topological numbers for topo- logical classification.



Experiment on seismic behavior of prefabricated concrete composite beam-column joint connected by steel

ZHANG Qifan, ZHU Jiejiang

2024, 30(1):  118-127.  doi:10.12066/j.issn.1007-2861.2415

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Based on the existing researches regarding prefabricated joints conducted domestically and abroad, this study proposed a prefabricated concrete composite beam- column joint connected by steel. Low cycle repeated loading tests were conducted to study the seismic performance of the proposed joint. The experimental results show that the stress can be effectively transferred between the steel joint and longitudinal bar of the precast beam. Moreover, the composite beam-column joint has good integrity. The plastic hinge of the joint is located near the welded part of steel and longitudinal bars in the beam, and the damage inflicted on the core area of the beam-column joint is small. The novel joint exhibits good energy dissipation capacity. Compared with the cast-in-place joints, the proposed prefabricated joint has higher bearing capacity but lower ductility.



Deformation analytical solution for a retaining structure with an elastic support ring beam of a circular deep foundation pit

OUYANG Yu, GAO Yunfei, REN Kaikai

2024, 30(1):  128-139.  doi:0.12066/j.issn.1007-2861.2348

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A ring beam and its retaining structure are regarded as an elastic ring and an elastic thin cylindrical shell, respectively. In this study, based on the deformation compatibilities between the ring beam and cylindrical shell, an analytical solution for the deformation of a retaining structure of a circular deep foundation pit with any number of elastic ring beam supports is obtained. Based on the verified rationality and reliability of the analytical solution, this study compares the differences in deformation and internal force distributions of the retaining structure of a practical circular deep foundation pit with rigid and elastic ring beams, respectively. In addition, influence of parameters including bottom boundary conditions of the retaining structure, elastic modulus, size, number, and position of the ring beams on the deformation and internal force distributions of the retaining structure are studied. Results show that, compared with the internal force changes to the retaining structure with a rigid ring beam, those to the retaining structure with an elastic ring beam are relatively small. In addition, changes to the elastic modulus and size of the ring beam are found to have a significant effect on the deformation and internal forces of the retaining structure above the excavation surface of the foundation pit. However, they have little influence on the deformation and internal forces of the retaining structure below the excavation surface. These results provide a theoretical basis and guidelines for the design of a retaining structure of a circular foundation pit.



Analysis of progressive collapse resistance of through diaphragm bolted joints

MENG Yongqi, YANG Feng, WANG Yilun, WANG Hongwei

2024, 30(1):  140-151.  doi:10.12066/j.issn.1007-2861.2317

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A three-column two-span plane frame structure is designed based on a concrete- filled steel tubular diaphragm through bolted joints. The entire process of collapse is simulated by static loading, and the mechanical deformation, resistance mechanism, failure phenomenon, and strain development of the joints are investigated. An ABAQUS finite element model is established to analyse the structural failure mode. Experimental and finite element results show that the collapse process can be divided into four stages: beam mechanism, mixed action, catenary action, and failure. The collapse resistance of the structure depends on both the bending and tensile capacities. The designed joints can meet the rotation requirements of FEMA-365, and the catenary action in the structure occurs prior to the failure stage. In addition, structure component failure occurs at the lower flange of the middle node H-beam, and the hole wall tearing causes the crack to extend to the web plate, which in turn generates a fracture in the H-beam. Because of the weakening of the flanges by bolt holes, it is suggested that the flanges of bolted H-section steel should be strengthened to ensure the effectiveness of the connection.



Global warming research based on quantile regression model and empirical mode decomposition

XIAO Jie, AI Min, NI Zhongxin

2024, 30(1):  152-163.  doi:10.12066/j.issn.1007-2861.2293

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The purpose of this study is to analyze climate’s variation trend and forecast the climate. The main methods are known as quantile regression and empirical mode de- composition (EMD). Firstly, a global heat map is utilized for the descriptive statistics of global temperature data. The EMD method is applied for data denoising to analyze global temperature’s variation trend, and the concept of global temperature cycle is introduced. These aim to study the trend of global warming. Secondly, the multivariate linear regres- sion model and the quantile regression model are applied to identify factors influencing global temperature. Then the temperature model is built to predict temperature changes. The findings can provide statistical support for global climate analysis.



Analysis of large-diameter shield cutting through anti-slide pile and its effect on embankment deformation

JIANG Xiaotian, LI Zhanglin, HE Guojun, ZHANG Mengxi, ZHAO Huiling

2024, 30(1):  164-173.  doi:0.12066/j.issn.1007-2861.2425

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This study analyzed the disturbance effect on an embankment of large-diameter shield cutting through an anti-slide pile with the goal of ensuring the safety and stability of a levee during the process of shield tunneling. This paper shows how a three-dimensional tunnel–pile foundation–embankment numerical model was established using finite element analysis software. The settlement of a levee and deformation of piles during shield tunneling were analyzed, and the deformations of the piles under different shield thrust values were compared. The results showed that the cutting of anti-slide piles by a shield machine will significantly disturb the upstream slope of a levee. The largest longitudinal displacement occurred at the top of the slope, and the soil around the pile showed obvious settlement. Under the influence of the shield thrust and landslide thrust, the anti-slide pile was characterized by flexure deformation, which formed a slanting “S” curve. The deflection of the anti-slide pile was the most obvious when the cutter head of the shield machine was close to it. The thrust of the shield increased from 0.7 to 0.9 times the static earth pressure, the horizontal displacement of the pile significantly increased, and the displacement of the pile bottom increased by 162% when the cutter head approached the pile foundation. Therefore, when a shield machine cuts through an anti-slide pile, construction parameters such as the advancing speed and mud-water pressure should be strictly controlled to reduce the adverse effect of the shield thrust on the pile.



Local discontinuous Galerkin finite element method for the Caputo-type diffusion equation with variable coefficient

DAI Qiaoqiao, LI Dongxia

2024, 30(1):  174-190.  doi:10.12066/j.issn.1007-2861.2426

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We present an efficient method for seeking the numerical solution of a Caputo- type diffusion equation with a variable coefficient. Since the solution of such an equation is likely to have a weak singularity near the initial time, the time-fractional derivative is discretized using the L1 formula on nonuniform meshes. For spatial derivative, we employ the local discontinuous Galerkin method to derive a fully discrete scheme. Based on a dis- crete fractional Gronwall inequality, the numerical stability and convergence of the derived scheme are proven which are both α-robust, that is, the bounds obtained do not blow up as α → 1⁻. Finally, numerical experiments are displayed to confirm the theoretical results.